Measurements of the individual phase composition of petroleum, water and gas mixtures produced during oil production processes are used in well testing, well management, and production allocation. Conventional measuring devices for two and three-phase metering systems require expensive and cumbersome test separators, test lines, associated valving and instrumentation controls, safety systems and metering, especially for offshore/subsea wells and other installations, which require high maintenance, and field personnel intervention. Test separators may introduce environmental problems as well. Current approaches to multiphase metering are expensive and, consequently, meters are rarely used on a single well, but rather on a group of wells that route their productions to gauging stations with large manifolds to accommodate many wells. Each well is tested sequentially for a brief period of time. In some oil fields, produced multiphase fluid is first passed through a cyclone type of gas-liquid separator before directing the liquid to an oil-water measuring system. There are many instruments available to make two-phase (oil-water) composition measurements that include capacitive, microwave, Coriolis, and ultrasonic measurements. There is presently no commercially available, inexpensive and reliable instrument suitable for single well testing.